Method for manufacturing a tire having the sidewalls ends overlapping the ends of the tread band

ABSTRACT

A method and apparatus for manufacturing a tire in which the sidewalls overlap the ends of the tread band. The method comprises the steps of inserting an extensible tubular releasing element around the carcass plies at each end of an assembly drum, wrapping the sidewalls on these elements, applying another tubular element on the sidewalls, and overturning the tubular elements to spread apart the sidewalls in an open position aside of the assembly drum. The carcass, in the form of a first-step cylindrical sleeve comprising open sidewalls, is transferable to a (second-step) forming drum to be torically formed against a separately prepared assembly comprising the belt pack and the tread band. Next, the band ends are turned down onto the toric carcass and the sidewalls are folded back against the carcass and over the ends of the tread band.

FIELD OF THE INVENTION

The present invention relates to a method for manufacturing a tire and,more specifically, to a method for manufacturing a tire having sidewallsenclosing the ends of the tread band, as well as to an apparatus forcarrying out this method and to a tire thus produced.

BACKGROUND OF THE INVENTION

As is known, a tire essentially comprises a carcass including at leastone reinforcing ply, a couple of bead wires around which the ply edgesare folded back in loop form after interposition of an elastomericfilling fixed to the radially external surface of each bead wire, abelting structure arranged as a crown around the torically formedcarcass, a tread band wrapped around the belt, and a couple of axiallyopposed sidewalls, radially extending between the bead wires and thetread band.

Some kind of tires have the side portions of the tread band arrangedover the radially external end of the sidewalls, while in other kindsthe upper ends of the sidewalls are overlapped on the ends of the treadband.

A conventional tire manufacturing method substantially comprises thesteps of wrapping at least one carcass ply around a cylindrical assemblydrum having a radially external surface connected to correspondingaxially external side surfaces, perpendicular to the drum rotation axis,through two curvilinear connecting surfaces, preferably arc-shaped intransversal cross-section, said ply having a width greater than that ofthe drum; turning down the edges of the ply radially inwardly onto thedrum side surfaces, fixing the bead wires, optionally already assembledwith the corresponding filling, against the carcass ply edges at saidside surfaces of the drum, folding back the carcass ply edges in loopform radially outwardly around the bead wires and against the carcassply, preferably until they reach and cover a portion of the ply lying onthe cylindrical surface of the drum, wrapping around the side portionsof the carcass ply, on the cylindrical portion, the correspondingsidewall of the tire with the axially external edge laterally protrudingfrom the drum for a part sufficient to reach the bead wire zone,pressing the sidewall against the carcass ply to produce in this mannera semi-finished product commonly known as a cylindrical carcass sleeve.

Subsequently, the above mentioned sleeve is withdrawn from the assemblydrum (or first-step drum) after contraction of the drum and fitted ontoa toric forming drum of the expanding type (or second-step drum) toassociate the same with the belt pack and the tread band which wereseparately preassembled on an auxiliary assembly drum.

To implement this second operating step, after fitting the sleeve ontothe forming drum the belt/tread band assembly is placed around thesleeve in coaxial alignment with its center-line plane (or equatorialplane of the tire) and air is fed under pressure into the sleeve totorically form the same until the crown zone of the sleeve is broughtagainst the belt pack.

Subsequently, the coupling between the sleeve and the belt/treadassembly is improved with appropriate pressing means to provide a greentire which will then be inserted in a mold to form the tread pattern andvulcanize the tire.

It is commonly known and in any case clear from the above that in thecase of tires provided with sidewalls closed on the ends of the treadband the method described above requires modification to allow pressingof the tread band against the carcass ply before the sidewalls areoverlapped on the side portions of the tread band.

In practice, the following procedure is followed. In the step ofconnecting the sidewalls to the cylindrical carcass sleeve ananti-adhesive element, usually a strip of sheet material (e.g.polyethylene), is preliminarily wound around the carcass ply towardseach end of the drum for a portion of predetermined width so as toprevent adhesion of the ply to the entire surface of the sidewalls whichare subsequently overlapped around each anti-adhesive element with theiraxially internal edge on said anti-adhesive element, while taking carethat the sidewall portion between their axially external edge and theaxially external edge of the anti-adhesive element be wide enough toensure adhesion of the sidewall to the carcass in order to preventrelative sliding between the sidewall strip and the carcass ply duringrotation of the assembly drum.

Next, after jointing together the ends of the sidewall portion depositedon the carcass and pressing the zone of the axially external edge of thesidewall against the carcass ply, said sleeve is removed from theassembly drum and fitted on the forming drum (i.e. the second-stepdrum), wherein the anti-adhesive element interposed between the sidewalland the carcass is withdrawn. This withdrawal is necessary to be able toassociate the corresponding axially internal surface of the sidewallswith the carcass ply and over the side surfaces of the tread band.

The operation is manually or mechanically carried out primarily bygradually spreading apart the sidewalls from the carcass sleeve and thenby removing the anti-adhesive element: preparation and subsequentrolling of the belt/tread assembly against the carcass ply are thenperformed and, lastly, the sidewalls are overturned from thespread-apart position to a closed position against the carcass ply andthe ends of the tread band.

The method described is a source of a number of considerableshortcomings: in the first place, the step of spreading apart thecarcass sidewall involves a radial stretching of the sidewall,perpendicularly to the tire rotation axis, with ensuing harmfuldimensional variations of the semi-finished product, due to theplasticity of the material in the green state, which are very seriousand sometimes unacceptable when the spreading operations of the sidewallare carried out manually. More particularly, the sidewall takes on anirregular wavy configuration predominantly concentrated along itsperiphery.

In addition, after the spreading apart operations, the free part of thesidewall no longer supported by the carcass wall in toric configuration,tends, due to its memory, to gradually return to a configuration freefrom internal stresses, i.e. a configuration corresponding to thedeposition diameter of the sidewall onto the cylindrical surface of theassembly drum.

Consequently, there is a tendency of the radially external sidewall edgeto curl axially outwardly on itself and against the radially internalportion which is already permanently fixed to the carcass ply and in anycase to take on an irregular geometrical configuration in an axialdirection.

This fact prevents the subsequent overturning of the sidewall inextended form against the carcass and the side portions of the treadband.

The operation is normally performed either manually or with the aid ofrollers or through expansion of two small inflatable chambers arrangedaside of the forming drum which, in their expansion, come into contactwith the sidewall guiding its overturning against the carcass. In thesituation just described, the sidewall overturning operation oftenoriginates a further undesired folding of the sidewall and in any caseconsolidates the curling and folding which may have possibly formed,which must be eliminated by using specific manual work with resultingcost increases of the manufacturing method and quality deterioration ofthe finished product.

Lastly, the removal of the anti-adhesive element, in particular whenthis is a thin sheet of plastics such as a strip of polyethylene is oneof the most delicate operations in the tire manufacture, up to the pointthat the final result of this removal can determine the acceptability ofthe tire.

Indeed, it is to be noted that the anti-adhesive element is insertedbetween the sidewall and the carcass ply and thus creates with itsradially internal edge the weld line between the sidewall and thecarcass so that it may turn out to be as clamped between these elements.

In the removal step of the element consisting of the above mentionedsheet the forces applied by the operator may cause by tearing anentrapment of small sheet scraps between the sidewall and the carcass:the result is a welding failure between the rubber compositionsseparated by these scraps during the subsequent vulcanization step ofthe tire. The ensuing detachments in the tire may cause during operationa rapid destruction of the tire.

A last but no less important drawback, is that the generalized use ofanti-adhesive elements of undegradable and unrecyclable materials, suchas e.g. polyethylene, causes problems of environmental pollution due tothe wasting of numberless releasing strips no longer reusable in theindicated production method.

SUMMARY OF THE INVENTION

The manufacturing method of the present invention is specificallydirected to manufacturing the type of tire described above and tosolving the problems set forth above.

The aim of the present invention is to provide a method formanufacturing a tire of the type having sidewalls overlapping the sideportions of the tread, capable to achieve greater automation of themanufacturing cycle with reduced manufacturing costs, high quality ofthe finished product, without the risk of trapping incompatiblematerials within the tire body and discharging non-reusable servicematerials.

In a first aspect, the present invention relates to a method formanufacturing a tire having the sidewall ends overlapping the ends ofthe tread band starting from a cylindrical sleeve-shaped tire carcasscomprising at least one carcass ply provided with reinforcing cordshaving respective ends each folded back around at least onecircumferentially inextensible bead wire and a tire sidewall fixed oneach side portion of said sleeve, said method comprising the steps of:

wrapping at least one carcass ply around an assembly drum having aradially external cylindrical surface connected to correspondingradially external side surfaces through two curvilinear surfaces, saidcarcass ply having a width greater than the width of said drum,

radially and inwardly turning down the edges of the ply onto said sidesurfaces of the drum,

fixing said bead wires against said edges of the carcass ply at saidside surfaces,

folding back the edges of the carcass ply in loop form radially andoutwardly around the bead wires and against the carcass ply,

arranging an anti-adhesive element around the side portions of saidcarcass ply on the cylindrical portion and for a part of predeterminedwidth,

wrapping around each anti-adhesive element the corresponding sidewall ofthe tire with the axially internal edge on said anti-adhesive elementand with the axially external edge laterally protruding with respect tothe corresponding axially external edge of said anti-adhesive element,

pressing the portion of said sidewall laterally protruding from theaxially external edge of the anti-adhesive element against thecorresponding ply portion and/or folded back ply portion of the carcassply, and

withdrawing said cylindrical sleeve carcass from said assembly drum forfurther finishing operations of the tire,

said method being characterized in that it makes use as theanti-adhesive element of a first tubular element, coaxial with saiddrum, radially extensible and axially inextensible, axially movable inboth directions from a first position away from said drum to a secondposition wherein it fits thereon.

Preferably, this method comprises the additional step carried out beforewithdrawing said sleeve from said drum, of drawing the axially internaledge of said first tubular element axially and outwardly until saidsidewalls are completely spread apart from said carcass.

Still more preferably, this method is characterized in that additionalanti-adhesive means are arranged on the outer surface of said sidewalls,said additional anti-adhesive means comprising a second tubular elementwhich is radially extensible and longitudinally inextensible, axiallymovable in both directions from a first position away from said drum toa second position wherein it fits thereon.

Again preferably, the method is characterized in that the sidewalls andthe carcass ply are made mutually integral before rotating the drum in aknown manner to wrap the sidewalls onto said sleeve.

This step may be conveniently carried out with removable clamping meansin the form of clamps and the like, arranged at least in two axiallyopposed positions of the drum revolution surface. Advantageously, theclamping means ensure freedom from relative slipping between the tubularelement and the sidewall during the wrapping step of the sidewalls ontothe sleeve surface.

In a preferred embodiment, the method is characterized in that saidfirst tubular elements are fitted on said drum by bringing theaxially-free external edge of said tubular elements at the curvilinearconnecting surfaces between said radially external cylindrical surfaceand the corresponding axially external surfaces of said drum.

In another aspect, the present invention relates to an apparatus formanufacturing a cylindrical sleeve-shaped tire carcass, as describedabove, comprising an assembly drum, rotating around its own axis, havinga radially contractable radially external cylindrical revolution surfaceconnected to two axially opposed external side surfaces through twocurvilinear surfaces, means for turning down and folding back the endsof said plies on said side surfaces and means for setting bead wiresagainst said side surfaces, which is characterized in that it comprisesaside of each drum end at least a first anti-adhesive element,comprising a tubular part having a maximum diameter equal to the drumdiameter, coaxial with said drum, open as a funnel at one end, at leastone annular flange, coaxial with the drum, having an internal diametergreater than the diameter of said drum, rotatably connected to the drumand axially movable in both directions with respect thereto, saidannular flange being connected with the funnel-shaped end of saidelement, and means for axially moving said flanges.

Preferably, the apparatus is characterized in that it comprises, foreach end of said drum, a couple of said tubular elements, coaxial andconcentric with one another, each connected to a corresponding annularflange: each element, having a funnel-shaped tubular form and unbrokensurface, is conveniently made of an anti-adhesive material havingextensibility characteristics in a circumferential direction andinextensibility characteristics in an axial direction ensured byreinforcing means incorporated and appropriately positioned in saidtubular elements.

In a first embodiment, the above mentioned element is made of arubberized fabric cylinder reinforced with threads selected from thegroup comprising monofilaments, elementary threads and reinforcingcords, arrange textile or metallic, arranged in a mutually parallelmanner according to the generating line of said cylinder.

In an alternative embodiment, the above mentioned element is made of arubber tube incorporating reinforcing fibers selected from the groupcomprising axially-oriented textile, metallic or glass fibers.

In a different aspect, the present invention also relates to a tire forvehicle wheels comprising a torically shaped carcass, provided in aradially internal position with beads for anchoring to a correspondingmounting rim, a tread band crown-arranged around the carcass having endswelded to the underlying carcass ply and a couple of axially opposedsidewalls, extending in radial direction from the zone of the bead wiresup a zone wherein they cover the side ends of the tread band,characterized in that said sidewalls have been folded back against saidside ends of the tread band by the method of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be anyhow better understood with the aid ofthe following description as well as of the annexed drawings, givenbelow by way of non-limiting illustration, in which:

FIG. 1 shows a cross section of a tire according to the prior artwherein the side portions of the tread band are enclosed between theupper ends of the sidewalls,

FIGS. 2 through 8 show partial cross sections of a known assembly drumon which a tire carcass sleeve manufactured in accordance with themethod of the present invention is being completed with the aid of thenew apparatus with releasing tubular elements, and

FIGS. 9 and 10 show, in two partial cross sections, the transfer, toricconformation and completion steps of the sleeve of FIG. 8.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS

To better clarify the following description, FIG. 1 initiallyillustrates the type of tire which may specifically be made by themanufacturing method of the present invention; this tire comprises atorically-shaped carcass 2 comprising at least one reinforcing ply 3,the edges 3' of which are folded back in loop form around usual beadreinforcement wires 4.

Rubber fillers 5 are arranged in a known manner between the ply 3 andthe associated folded back edges 3'.

For the purposes of the present invention, the carcass may indifferentlybe either of the radial type or of the crossed-ply type.

The tire 1 also comprises, crown-arranged around the carcass 2, a treadband 10 the ends of which are welded to the underlying carcass ply.Inserted between the carcass and the tread band a belt pack may beprovided, consisting of at least two radially superimposed belt strips7, 8, provided with parallel reinforcing cords in each strip andinclined with respect to the equatorial plane of the tire, preferablysymmetrically crossed with one another and preferably reinforced by afurther radially external layer 9 with circumferentially-orientedreinforcing cords. All the used materials are conventional and may beselected by the skilled in the art on the basis of specific needs withreference to the type of tire and its performance, so that they are notfurther described.

The carcass is additionally provided with a pair of axially opposedsidewalls 11 extending in radial direction from the bead zone (from thebead wires) to cover the side ends of the tread band 10.

The method for manufacturing a radial tire of the type illustrated hasalready been described in the introductory part of this description, sothat specific reference is made hereinafter only to the modificationsintroduced in accordance with the present invention.

In greater detail, FIG. 2 shows an assembly drum 12 also know asfirst-step drum, having a radially external cylindrical revolutionsurface, radially contractable for disengaging the carcass sleeve builton the drum. For the sake of simplicity, the drawing figuresillustrating the different operating steps show partial cross sections,both axial and radial, of the assembly devices and of the tire beingmanufactured and do not illustrate the common frame, i.e. the apparatus,on which the above mentioned devices and the related acting means aremounted.

The cylindrical surface of the assembly drum 12 is connected to the twoaxially external side surfaces, generally at right angles to the drumrotation axis, also defined hereinbelow as drum shoulders, through twocurvilinear surfaces each preferably shaped according to an arc havingradius "r".

In accordance with the invention, aside of each end of drum 12 isarranged an annular flange, preferably a pair 19, 20 of annular flanges,coaxial with the drum 12 and having an internal diameter greater thanthat of the drum, synchronously rotating and separately axially movablein both directions with respect thereto.

Each flange is integral with one end of a tubular element 17, 18 free atthe other end and is fixed to a means for axial movement.

The tubular elements 17, 18 are coaxial and concentric with one anotherand comprise a geometrical figure identified by a tubular portion havinga diameter substantially equal to the drum diameter, which at one endopens like a funnel to engage with one of the above mentioned flanges.

For the sake of simplicity, in the drawing figures the means for theaxial movement of the flanges are not shown since they are of known typeand in an case readily determinable by one skilled in the art: forexample, they may consist of an apparatus with cylinder and piston withhydraulic or pneumatic control, having the function of displacing eachflange and, along therewith, the related tubular element, either towardsthe assembly drum or towards the opposite direction.

Each element has a tubular and funnel-like shape with unbroken surfaceand is made of an anti-adhesive material with elasticity characteristicsin the circumferential direction but substantially inextensible in theaxial direction, for the purpose of being able to expand for wrappingup, optionally under pressure if desired, cylindrical bodies placedtherein and to withstand longitudinal traction without elongation.

The aforementioned tubular elements are preferably made of rubber havinganti-adhesive characteristics with respect to the materials of the tirecarcass with which they will be in contact, e.g. with silicone-basedrubber compositions, and preferably incorporate continuous ordiscontinuous reinforcement means arranged in such a way as to providethe above-mentioned circumferential extensibility and axialinextensibility.

In a preferred embodiment, the anti-adhesive element is made of acylinder of rubberized fabric, reinforced with threads selected fromeither textile or metallic monofilaments, elementary threads and cordsmutually arranged in parallel with one another and essentially inaccordance with the generating line of the cylinder. Those skilled inthe art will have no difficulty in choosing any other reinforcingelement which appears to be most suited to his specific requirements.

Optionally, the reinforcing elements may not be incorporated in thetubular element and in a different embodiment they can be present on oneor both the surfaces of the tubular element, preferably also acting asanti-adhesive elements.

In another alternative embodiment, the element may be made of a rubbertube incorporating as reinforcing elements, e.g. textile, metallic orglass fibers, preferably oriented in an axial direction, uniformlydistributed in the tube wall.

The thickness and/or quantity of said reinforcing means is determined asa function of the stresses to which the element might be subjected inoperation and, more specifically, of the tensile stress to which it willundergo during the manufacturing steps of the carcass sleeve.

FIG. 2 also shows the cylindrical carcass sleeve during its assembly onthe drum 12 according to the procedures discussed above.

In practice, a sheet of impermeable rubber 2' and at least one carcassply 3, optionally preassembled together, are wrapped by rotating thedrum onto the cylindrical drum surface; the impermeable sheet, usuallycalled `liner`, has the function of ensuring air tightness in thefinished tire of the so-called tubeless type, i.e. those which are usedwithout inner tubes.

Next, through a folding apparatus, not shown being known per se, the plyedges protruding from the drum are turned down radially and inwardly onthe shoulders 13 of the above mentioned drum: then through a bead-wiresetting apparatus, known per se and not shown, the assembly comprisingthe bead wire 4 and the rubber filling 5 mounted on its radiallyexternal surface is pressed against the carcass ply at the drum shoulder13.

Finally, the edges 3' of the ply 3 are folded back in loop form radiallyfrom the inside outwardly around the bead wire and its filling,preferably up to covering part of the carcass ply at the centralcylindrical portion of the drum.

It is clear that the bead zone may comprise other structural elements,such as loops, edges and additional reinforcements, all known per se,which are not described here bearing no influence with respect to thepresent invention.

Now the strips of elastomeric material constituting the tire sidewallsare mounted on the cylindrical sleeve. According to the presentinvention, to implement this step the axially most inward flange 19 isaxially moved along (FIG. 3) the direction of arrow F1, around theassembly drum thus dragging the tubular element 17 onto the carcasssleeve, continuing the movement at least until the axially external edge21 of said element is also correctly positioned on the sleeve asexplained below.

Since the internal diameter of the tubular element is selected so as tohave a value proximate to but not greater than that of the assembly drumdiameter, the element slightly expands, point by point, in relation tothe thickness of the sleeve fitted on the drum, which is variable from aminimum at the cylindrical portion of the carcass ply up to a maximum atthe ply folds and thus wraps up the sleeve with a slight pressure.Preferably, the expansion values of the element do not exceed 10% of itscircumferential development.

Still more preferably, the above mentioned axial movement in relation tothe length of the tubular element continues until the free end 21, i.e.the axially external edge of the element, reaches the connecting arc 14between the cylindrical surface and the drum shoulders.

The length of the cylindrical part of the tubular element, i.e. of thetubular element part between the beginning of the funnel-shapedportion--connecting the element to the corresponding displacingflange--and the axially external edge, allows to use said tubularelement with different widths of the tire sidewalls, in such a way thatit does not require its substitution along with the size of the tirebeing built, as will be clarified hereinbelow.

Preferably, the position of the above mentioned edge 21 of the tubularelement is identified by the intersection of the surface of theconnecting arc 14 with the conical surface defined by the radius of saidarc 14 when the angle α between the drum rotation axis and the radius,i.e. the cone opening, is between 0° and 90°.

Preferably, the angle α is between 15° and 60° and, still morepreferably, is equal to 45° in such a manner that after overturning thearrangement of the sidewall aside of the drum keeps the same diametervalue of its configuration upon deposition on the drum.

Now the free ends of the two strips of the sidewall (FIG. 4) are fixedon the carcass sleeve over the corresponding tubular elements and theassembly drum is rotated so as to drag and wrap onto the externalsurface of each element 17 the related tire sidewall 11, withdrawn froma special dispenser (not shown) arranged near the drum.

It is clear that the sidewall portion in direct contact with the carcasssleeve, i.e. the sidewall portion between the axially external edge ofthe tubular element and the axially external edge of the sidewall, mayhave a so narrow width as not to ensure that rotation of the drum willdrag out and wrap the sidewall strip thereon, especially when, inaccordance with the above mentioned preferred embodiment of the presentinvention, the edge of the element lies on the end of the drum.

In this case, before starting drum rotation, the free ends of thesidewalls are conveniently blocked on the sleeve with removable devices,known per se, e.g. of the clamp type, arranged on the drum shoulderspreferably at axially opposed positions.

Upon completion of drum rotation and after having joined together thetwo sidewall ends, the sidewalls 11 (FIG. 5) are turned down on the drumshoulders 13, e.g. in accordance with solutions and by means of rollingdevices which, being part of the prior art, are not further described indetail.

The carcass sleeve is now ready to be removed from the drum and sent tothe forming step after removal of the tubular element and spreadingapart of the sidewall as discussed below. However, in accordance withanother preferred embodiment of the method according to the invention,another operating step is provided which is carried out on the assemblydrum using the second tubular element mentioned above.

More specifically, the second tubular element 18 is displaced, accordingto an axial movement along arrow F1 shown in FIG. 6, towards theassembly drum until it is fitted on the outer surface of the sidewall 11which in this manner is clamped between the couple of tubular elements17, 18.

Clearly, this is made with both sidewalls, and the element 18 as well,which is fully equivalent to element 17, surrounds the sidewall with aslight pressure linked to the expansion (maximum value 10%) undergoneduring the step of fitting on the sidewall.

Next, in a further step and again in accordance with the invention, themeans for axially moving the two tubular elements 17, 18 are operatedsimultaneously and axially towards the outside of the drum along thedirection of arrow F2 shown in FIG. 7.

As shown in FIG. 7, the above mentioned axial movement of the tubularelements overturns the sidewall 11 axially towards the outside for theentire portion which could not adhere to the sleeve surface thanks tothe interposition of the tubular element 17.

Advantageously, when the sidewall adheres to the sleeve only at thecurvilinear connecting portion with the drum shoulders, according to theabove mentioned preferred embodiment, upon overturning it takes on anessentially cylindrical configuration having a diameter corresponding tothat of the drum as shown in FIG. 8, i.e. it is arranged according to anessentially stable configuration because its elastic memory can donothing but compel said sidewall to return to the configuration it hadupon deposition on the drum, i.e. a cylindrical configuration which isin practice aside and coaxial with the drum surface.

The carcass sleeve having spread-apart sidewalls thus formed, is removedfrom the assembly drum after radial contraction of the same andtransferred into the second-step operating area, preferably directlyonto the second-step drum by means of a transferring apparatus 23 (FIG.9) comprising adequate sleeve-supporting means known per se.

During the second-step operations and after rolling of the belt/treadband assembly against the carcass ply as described above, inflatableside chambers 28 overturn the sidewalls 11 on the carcass and on theside portions of the tread band and it is clear that the cylindricalform of the sidewalls obtainable by the method of the present inventionallows to carry out this overturning in an optimal manner, withoutcausing undesired deformation or irregular stretching of the sidewall.

The method of the present invention achieves the desired results.

First of all, it can be noted that the use of the second tubular element18 in a position radially external to the sidewall is preferred but notessential, since spreading apart of the sidewall may already be achieved(FIG. 8) with the first tubular element 17.

Indeed, the tubular element, although being made of a releasing materialinsensitive to the stickiness of the green materials of the carcasssleeve, cannot be removed from beneath the sidewall following the axialmovement towards the outside of the guide flange, since the axiallyinternal end of the sidewall does not offer sufficient mechanicalresistance to constitute a constraining element around which the tubularelement could slip while revolving around itself: in conclusion, theoverturning of the tubular element consequently causes overturning ofthe sidewall.

This overturning only allows expansion in a circumferential directionfor the tubular element but does not involve elongation in an axialdirection, which is prevented by the presence of the inextensiblereinforcing elements of said element so that it ensures dimensionalstability of the sidewall width, which sidewall cannot undergostretching in the same direction in its overturning movement.

The preferred use of the second tubular element 18, in addition tofacilitating overturning of the sidewall which is clamped between thetwo tubular elements, most favorably ensures that the overturningportion of the axially external surface of the sidewall does not touchthe surface portion of the same sidewall still lying on the drum, sincethe two above mentioned portions of the same sidewall surface areseparated by the tubular element 18.

Basically, the tubular element 18 acts as a lubricating substance withthe result of allowing the sidewall 11 (FIG. 7) to freely slide towardsthe opening position shown in FIG. 8. The skilled in the art will haveno difficulty in replacing the element 18, if preferred, with otheralternative anti-adhesive means.

The weld line position between the sidewall and the sleeve at thecurvilinear connection between the cylindrical surface and the drumshoulders is also to be considered as preferred, since a differentposition, in particular an axially more inward one, does not preclude tocarry out a correct spreading apart of the sidewall in a uniform mannerand without irregular stretching of the material: on the other hand, thespread-apart sidewall being arranged along a surface having a diametergreater than that of deposition on the drum, maintains an internaltension state which tends to close the axially outermost free endtowards the drum rotation axis.

The use of tubular elements employed in the steps of the present methodallows, as explained above, to abandon the conventional anti-adhesiveelements in sheet form inserted between the carcass ply and thesidewalls during the manufacturing steps of the carcass sleeve.

Thus, the shortcomings of the prior art connected to scraps of suchsheets (e.g. polyethylene) incorporated in the monolithic structure ofthe vulcanized tire are overcome.

In addition, thanks to the fact that the tubular element is re-usablefor a great number of manufacturing cycles of tires of various sizes,the problems, not only environmental, caused by the use of ever newsheets of releasing material for each tire to be manufactured and by theneed of disposing the same later at the end of the manufacturing cycle,are overcome.

More particularly, it is emphasized that one and the same tubularelement, being radially extensible, may be employed for a large range ofsleeves of different diameter, thus avoiding the need to changefrequently equipment for different tire sizes.

In addition, the tubular elements being already prepared in the correctform instead of being in sheet form, may be connected to automaticdisplacing devices capable to insert and withdraw the tubular elementsinto and from a cylindrically-shaped body within the same, such as acarcass sleeve wrapped on an assembly drum.

The steps of applying the releasing and sidewall fold-back element,therefore, may advantageously be automated with a number of qualitativeand economic benefits for the production process.

It is clear that the step of spreading apart the sidewall may beperformed even after having disassembled the sleeve from the first-stepdrum by providing appropriate clamping and releasing means for theaxially internal edge of the tubular elements from respectivedisplacement flanges which allows to move the sleeve with the tubularelements still inserted therein.

Advantageously, the method of the present invention allows to spreadapart the sidewalls aside of the sleeve in a stable tubular form,substantially aligned with the assembly drum surface. Thanks to theabove mentioned feature, the step of overturning the sidewalls performedon the forming drum against the toric carcass takes place correctly. Thechambers 28 aside of the forming drum, in fact, are positioned (FIG. 10)below the surface of the sidewalls arranged in a stable and extendedtubular configuration, free from curlings or similar irregularities.

During the overturning step, therefore, the chambers may gradually andregularly act on the sidewalls pressing them against the wall of thecarcass and of the tread band.

Finally, it is clear that the present description has only anexplanatory and non-limiting function so that those skilled in the art,after understanding the invention as described above, will be able toperform all those variations, modifications and replacements of thevariables associated with the present invention for the purpose ofsatisfying specific requirements.

I claim:
 1. Method for manufacturing a tire having sidewall endsoverlapping the ends of a tread band, starting from a cylindricalsleeve-shaped tire carcass comprising at least one carcass ply providedwith reinforcing cords having respective ends each folded back around atleast one circumferentially inextensible bead wire and a tire sidewallfixed on each side portion of said sleeve, said method comprising thesteps of:wrapping at least one carcass ply around an assembly drumhaving a radially external cylindrical surface connected tocorresponding axially external side surfaces through two curvilinearsurfaces, said carcass ply having a width greater than the width of saiddrum, radially and inwardly turning down the edges of the ply onto saidside surfaces of the drum, fixing said bead wires against said edges ofthe carcass ply at said side surfaces, folding back the edges of thecarcass ply in loop form radially and outwardly around the bead wiresand against the carcass ply, arranging an anti-adhesive element aroundeach side portion of said carcass ply on a cylindrical portion and for apart of predetermined width thereof, wrapping around each anti-adhesiveelement the corresponding sidewall of the tire with the axially internaledge on said anti-adhesive element and with the axially external edgelaterally protruding with respect to the corresponding axially externaledge of said anti-adhesive element, pressing a portion of said sidewalllaterally protruding from the axially external edge of the anti-adhesiveelement against the corresponding ply portion and/or folded back plyportion of the carcass ply, and withdrawing said cylindrical sleevecarcass from said assembly drum for further finishing operations of thetire,wherein each anti-adhesive element comprises a first tubularelement, coaxial with said drum, radially extensible and axiallyinextensible, axially movable in both directions from a first positionaway from said drum to a second position wherein it fits thereon.
 2. Amethod according to claim 1, wherein said first tubular elements arefitted on said drum by bringing an axially-free external edge of saidtubular element to the curvilinear connecting surfaces between saidradially external cylindrical surface and the corresponding axiallyexternal side surfaces of said drum.
 3. A method according to claim 2,wherein said free edge of said first tubular element is brought to theintersection between said curvilinear connecting surface and the conicalsurface generated by the radius of said curvilinear surface rotatingaround the drum rotation axis, said cone having an opening angle α offrom 0° to 90°.
 4. A method according to claim 3, wherein said angle αis between 15° and 60°.
 5. A method according to claim 1, it furthercomprising a step, carried out before withdrawing said sleeve from saiddrum, of drawing the axially internal edge of said first tubular elementaxially and outwardly until said sidewalls are spread apart from saidcarcass.
 6. A method according to claim 1, comprising applying as ananti-adhesive means on said sidewalls a second tubular element which isradially extensible and longitudinally inextensible, coaxial with saiddrum and axially movable in both directions from a first position awayfrom said drum to a second position wherein it fits thereon.
 7. A methodaccording to claim 1, wherein the sidewalls and said first tubularelement are made mutually integral before rotating the drum to causewrapping of said sidewalls onto said carcass sleeve.